Hypopyon is the accumulation of white blood cells within the liquid of the anterior (front) chamber of the eye. The cells are released from inflamed blood vessels located within the iris and tissues behind the iris.
When inflammation of the iris and ciliary body occurs (also called anterior uveitis), their blood vessels "leak" cells and protein into the anterior chamber. In small quantities, the accumulation of cells in the anterior chamber fluid results in a cloudy or hazy appearance to the eye. When inflammation is severe, larger quantities of white blood cells are released from iris blood vessels and gravity causes them to accumulate on the bottom of the chamber or fill it entirely. Hypopyon usually appears white-to-yellow in color. Some clumps of cells may stick to the back of the cornea, producing tiny specks on the cornea.
In addition to cells, certain proteins are released from inflamed blood vessels that transform into strands called fibrin within the anterior chamber. Fibrin is commonly observed with hypopyon in eyes with severe anterior uveitis.
Hypopyon can develop in any eye with severe uveitis. For that reason, hypopyon represents a symptom of serious ophthalmic disease. Hypopyon is often caused by bacterial infections of the eye, or by systemic viral, fungal, bacterial, parasitic and protozoal infections that may manifest in the eyes. Therefore, diagnostic tests are often essential in determining the underlying cause of this symptom.
Severe corneal ulceration also results in hypopyon. What to Watch For Evidence of eye pain
Dramatic color change, often yellow or cloudy, on the surface of the eye or within the anterior chamber
Difficulty in viewing details within the eye
Reduced vision or blindness
Reddened or "bloodshot" conjunctiva
White, gray or dark spots on the back of the cornea
Excessive squinting and blinking
Increased ocular discharge, especially watery or thick yellow-green discharge
Possible swelling of the eyelids
Diagnostic tests for hypopyon may include:
Physical examination to determine the presence of a systemic ailment that is manifesting within the eyes, and a history of prior or on-going treatment of a systemic or ophthalmic disease.
Complete ophthalmic examination including close scrutiny of the anterior chamber, tonometry to evaluate for the presence of glaucoma, fluorescein staining of the cornea to assess for the presence of ulceration, and examination of the structures in the back of the eye. Your veterinarian may refer your cat to a veterinary ophthalmologist for further evaluation using specialized instrumentation.
Ocular ultrasound examination may be performed when hypopyon obscures details within the eye or prohibits thorough examination of the structures in the back of the eye, particularly if there is no corneal ulcer present.
Your veterinarian may recommend other diagnostic tests on a case-by-case basis. Tests may include:
Complete blood count (CBC)
Serum tests for viral infections (e.g. feline leukemia, feline immunodeficiency, feline infectious peritonitis), cryptococcosis, or toxoplasmosis
Thoracic and abdominal radiographs (X-rays) may be recommended to determine the presence of lung disease (infection or cancer), organ enlargement and abnormal fluid accumulation.
Preliminary treatment for hypopyon is usually initiated while the results of specific diagnostic tests are pending. These include:
Aggressive therapy with topical and systemic antibiotics if a corneal ulcer is responsible for the hypopyon
Topical corticosteroids to reduce inflammation of the iris and ciliary body if anterior uveitis is responsible for the hypopyon and there is no corneal ulcer present
Topical treatment with 1% atropine to dilate the pupil, relieve pain, and decrease the chance of adhesions forming between the iris and the lens
Oral nonsteroidal anti-inflammatory medications, such as baby aspirin or ketoprofen, to reduce the uveitis. These may be used in the presence of many different types of infections.
Oral corticosteroid medications, such as prednisone. These medications provide strong anti-inflammatory effects, but are contraindicated in the presence of most systemic infections and all corneal ulcers. They are NOT prescribed until important diagnostic tests are completed that exclude a systemic infection as the cause for the hypopyon, and the presence of a corneal ulcer is ruled out. Oral corticosteroids are often reserved for those rare cases that are not due to infections and do not respond to other medications.
Treatment for glaucoma (elevated pressure within the eye) in some eyes with severe hypopyon. See the Client Education article on the Glaucoma in the Cat.
Do not delay in bringing the cat to a veterinarian for examination as most causes of hypopyon are potentially vision threatening and require immediate medical attention.